The present invention is directed to a method and apparatus that matches a recognized identifier based on a user-provided identifier to a reference identifier that is selected from a global set of reference identifiers, and, in particular, to a method and apparatus that prunes the set of reference identifiers each time a user rejects a matched reference identifier by excluding the rejected reference identifier from being compared to the recognized identifier in a subsequent comparison.
Most institutions, such as banks, department stores, and airlines, allow customers to access over the telephone a wide variety of services and information. Before the advent of touch-tone telephones, a customer would obtain these services and information through interacting with a live operator. As touch-tone telephones became more prevalent in homes, these institutions began switching to automated customer-access systems. After dialing a telephone number, a customer using such systems would be asked to enter an account number, or some other identifier. The user would enter the account number through the keys of a touch-tone keypad. As used herein, the term "identifier" refers to a string of characters that may comprise a plurality of letters, numbers, or both; based on this definition, an identifier may comprise either a random aggregation of characters, an actual word, or the name of a place or a person. Furthermore, as used herein, an identifier may comprise, but is not limited to, a string of characters for identifying a particular product, service, location, or account information.
Today, a user can provide such an identifier to an institution through a number of ways besides touch-tone telephony, including by speaking the identifier into the telephone handset. When the user is prompted to speak the identifier, the institution uses a speech recognition system to produce a recognized identifier based on the spoken identifier. Regardless of how the user enters the identifier, however, once a recognized signal representative of the input identifier has been received at the institution, the institution must match the recognized signal with one of a plurality of pre-stored identifiers, which are also referred to as reference identifiers. The complete set of reference identifiers is referred to as a grammar, or grammar domain. After a match between the input identifier and a reference identifier is found, the institution performs a transaction based on the matched reference identifier, such as retrieving account information or ordering a specific product. Finding such a match may take some time, however, since institutions often maintain thousands, if not millions, of reference identifiers. Moreover, the more reference identifiers that an institution must search through in order to find a match with an input identifier, the less accurate this search becomes, especially when the reference identifiers are alphanumeric, which tend to be confused with one another. Matching input identifiers with the wrong reference identifiers at least leads to delays and customer dissatisfaction, and perhaps also to erroneous billing or even to divulging sensitive, confidential information. What is therefore needed is a system that maintains a high degree of accuracy in matching input identifiers with reference identifiers, even when the total number of reference identifiers is quite large.